Fuel cell powered aircraft with a cathode convertible between oxygen and air and method for use thereof

ABSTRACT

An aircraft that includes a fuselage, an electric motor driven propulsion system, and a fuel cell system configured to provide electricity to the electric motor. The fuel cell system includes a fuel cell, a hydrogen tank, an oxygen tank, an air channel, and a cathode switch. The cathode switch being configured to convert between an air mode, wherein the fuel cell operates utilizing air from the air channel, and an oxygen mode, wherein the fuel cell operates utilizing oxygen from the oxygen tank.

BACKGROUND

Small unmanned aerial vehicles (“UAVs”), or drones, are usually batterypowered and are therefore limited in range by battery life. Hydrogenfuel cells are being considered as an option to extend range and flighttime of UAVs. Fuel cells operate by allowing an electrochemical reactionbetween hydrogen and oxygen, which produces electricity and water. Inmost fuel cell powered vehicles, hydrogen fuel, stored in an onboardhydrogen fuel tank, is supplied to an anode of the fuel cell and ambientair is supplied to a cathode of the fuel cell, the electricity produceddrives the motor and the water is disposed of. The reduced concentrationof oxygen in the air at higher altitudes creates an operational ceilingof about 15,000 feet for a fuel cell powered UAV.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a fuel cell powered UAV according tothis disclosure.

FIG. 2 is a perspective view of the fuel cell powered UAV of FIG. 1,showing some internal components.

FIG. 3 is a schematic view of a fuel cell system of the UAV of FIG. 1.

DETAILED DESCRIPTION

While the making and using of various embodiments of this disclosure arediscussed in detail below, it should be appreciated that this disclosureprovides many applicable inventive concepts, which can be embodied in awide variety of specific contexts. The specific embodiments discussedherein are merely illustrative and do not limit the scope of thisdisclosure. In the interest of clarity, not all features of an actualimplementation may be described in this disclosure. It will of course beappreciated that in the development of any such actual embodiment,numerous implementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother.

In this disclosure, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of this disclosure, the devices, members,apparatuses, etc. described herein may be positioned in any desiredorientation. Thus, the use of terms such as “above,” “below,” “upper,”“lower,” or other like terms to describe a spatial relationship betweenvarious components or to describe the spatial orientation of aspects ofsuch components should be understood to describe a relative relationshipbetween the components or a spatial orientation of aspects of suchcomponents, respectively, as the device described herein may be orientedin any desired direction. In addition, the use of the term “coupled”throughout this disclosure may mean directly or indirectly connected,moreover, “coupled” may also mean permanently or removably connected,unless otherwise stated.

This disclosure divulges a fuel cell powered aircraft with a cathodeconvertible between oxygen and air and a method for use thereof. Theaircraft generally includes a propulsion system driven by an electricmotor and a fuel cell system configured to provide electricity to powerthe electric motor. The fuel cell system includes a fuel cell with ananode and a cathode. The anode receives hydrogen from a hydrogen fueltank. Whereas the cathode may alternatively receive either ambient air,oxygen received from an oxygen tank, or a mixture thereof. A cathodeswitch converts between an air mode, wherein the cathode switch providesair to the cathode, and an oxygen mode, wherein the cathode switchprovides oxygen to the cathode. In alternative embodiments, the cathodeswitch may be associated with controlling the metering of oxygen addedto ambient air. The method of powering the propulsion system of anaircraft includes generating electricity from a fuel cell in the airmode and the oxygen mode and transmitting the electricity to theelectric motor of the propulsion system. In addition, the methodincludes autonomously converting between the air mode and oxygen modebased on flight parameters, atmospheric conditions, power demands, etc.,and may be optimized to maximize range and performance.

Operating a fuel cell on oxygen, rather than air, can increase the powerproduced by the fuel cell, at sea level, by 15 to 20 percent. Thepercentage of the power increase grows with altitude, where the amountof oxygen in the ambient air decreases. However, carrying an oxygen tankrequires carrying extra weight, which decreases range and performance.Accordingly, it may not be desirable to operate an onboard fuel cellexclusively using an onboard oxygen supply. As such, it may bepreferable to include an onboard oxygen supply that may vary in sizedepending on the particular mission. In order to minimize the addedload, the aircraft should preferably be operated in air mode when theambient air contains a sufficient oxygen content to enable the fuel cellto meet the power demands of the aircraft. As such, air mode shouldpreferably be the default operating mode. However, when air mode is notcapable of meeting the power demands of the aircraft, the aircraft mayautonomously convert to oxygen mode, thereby increasing the powergenerated by the fuel cell. This increased power may be needed, forexample, when taking off, when climbing, when flying above a certainaltitude, when flying at high speed, or to make evasive maneuvers. Whilethe aircraft is shown as, and the method is discussed for use with, aUAV, it should be understood that the aircraft and method described inthis disclosure could be utilized with any vehicle. It should beunderstood that even though oxygen is a component of air, when referringto “oxygen” in this disclosure it refers to a fluid having aconcentration of oxygen that is greater than that found in theatmosphere.

FIGS. 1 and 2 show a UAV 100 including a fuselage 102, a propulsionsystem 104 for providing thrust, a pair of wings 106 for providing lift,and a pair of stabilizers 108. Wings 106 and stabilizers 108 includeflight control surfaces (not shown) for controlling the attitude of UAV100. Propulsion system 104 includes a propeller 110 driven in rotationby an electric motor 112.

Referring to FIGS. 2 and 3, a fuel cell system 114 is shown. Fuel cellsystem 114 is configured to generate electricity to power electric motor112, as well as other onboard electronics. Fuel cell system 114 includesa fuel cell 116 having a cathode 118 and an anode 120, a hydrogen tank122 configured to store hydrogen therein, an anode channel 124configured to supply hydrogen from hydrogen tank 122 to anode 120, anoxygen tank 126 configured to store oxygen therein, an air channel 128,a cathode switch 130 in communication with oxygen tank 126 and airchannel 128, wherein cathode switch 130 is convertible between an airmode and an oxygen mode, and a cathode channel 132 configured to carryair or oxygen from cathode switch 130 to cathode 118.

It should be understood that fuel cell system 114 may comprise a fuelcell stack including a plurality of fuel cells 116. Fuel cell 116 maycomprise a polymer exchange membrane fuel cell or any other type of fuelcell suitable for use on an aircraft. Hydrogen tank 122 and oxygen tank126 may comprise cylindrical bottles, preferably made of a lightweightmaterial such as carbon fiber or aluminum and may be configured to storeliquified or compressed gaseous hydrogen and oxygen, respectively.Alternatively, hydrogen tank 122 and oxygen tank 126 may comprise anyother structures suitable for the storage of hydrogen and oxygen for usewith fuel cell 116. Air channel 128 may preferably comprise aforward-facing ram-air intake configured to increase the static airpressure of the air supplied to cathode 118. In addition, air channel128 may be used in conjunction with an onboard compressor (not shown)configured to compress ambient air for delivery to cathode 118.

UAV 100 also includes a processor 134 configured to control theconversion of cathode switch 130 between the air mode and the oxygenmode. Processor 134 may comprise an onboard computer for controllingflight of UAV 100, cameras, and/or weapons systems, or it may be aseparate component. Processor 134 may be configured to autonomouslyconvert cathode switch 130 between the air mode and the oxygen mode, itmay be configured to convert cathode switch 130 in response to a userinput requesting conversion, or it may be configured to do both.Processor 134 may be configured to convert cathode switch 130 from theair mode to the oxygen mode anytime power required by the electric motorexceeds the power generated by fuel cell 116 in the air mode. Forexample, if the user directs UAV 100 to accelerate and fuel cell 116 isnot capable of producing enough power to allow electric motor 112 toimpart sufficient rotational energy to propeller 110 to cause thedesired acceleration, processor 134 will autonomously convert cathodeswitch 130 to the oxygen mode, thereby providing the necessary increasein power production from fuel cell 116 to achieve the desiredacceleration. When the power required by electric motor 112 falls belowthe level that may be generated by fuel cell 116 in the air mode,processor 134 will autonomously convert cathode switch 130 back to theair mode in order to conserve the oxygen supply in oxygen tank 126. Thismethod of conversion control by processor 134 may be facilitated throughthe use of equations and/or lookup tables utilizing flight datatransmitted to processor 134 by a plurality of sensors (not shown). Forexample, the flight data may include altitude, air speed, rate ofacceleration, rate of climb or descent, attitude, etc., the flight datamay also include air data, such as angle of attack, air density, oxygencontent, etc. Utilizing this flight data, processor 134 may calculatethe required power to perform desired maneuvers, as well as the maximumpower that may be generated by fuel cell 116 in the air mode. Moreover,the sensors may include load sensors that transmit power usage data toprocessor 134.

Alternatively, processor 134 may be configured to convert from the airmode to the oxygen mode when certain conditions that are known torequire more power are satisfied. For example, processor 134 may causecathode switch 130 to convert to the oxygen mode when at least one ofthe following conditions are satisfied: (1) UAV 100 is operating above aknown altitude, (2) UAV 100 is moving faster than a known speed, and (3)UAV 100 is climbing faster than a known rate. Processor 134 may beconfigured to convert cathode switch 130 back to the air mode when thecondition(s) that caused the conversion to the oxygen mode is no longersatisfied.

There may be conditions in which the air mode may not be capable ofproducing sufficient power, but the full oxygen mode may not berequired. As such, it may be advantageous to configure processor 134 andcathode switch 130 to operate in a mixed mode, wherein cathode switch130 supplements the air from air channel 128 with oxygen from oxygentank 126 by simultaneously allowing the passage of air from air channel128 and allowing a variable amount of oxygen from oxygen tank 126 topass therethrough, based on real time power needs.

During operation, in addition to generating electricity, fuel cell 116creates heat and water. The water may be disposed of by simply allowingit to drain through a port in a bottom of fuselage 102. Alternatively,the water may be stored in a tank for future use, such as in a firesuppression system. The heat may be dissipated by an air cooling orliquid-cooling system. An air-cooling system may include air vents thatdirect ambient air through fuselage 102, past fuel cell 116. Inaddition, because fuel cell 116 may produce more heat in the oxygenmode, cathode switch 130 may be configured to redirect air flowingthrough air channel 128 to pass the exterior surface of, and therebycool, fuel cell 116 when cathode switch 130 is in the oxygen mode. Theliquid cooling system may include a pump powered by fuel cell 116 and achamber for circulating a coolant through fuel cell 116.

Because fuel cell 116 may not utilize all of the oxygen and hydrogendelivered to cathode 118 and anode 120, it may be desirable to includerecapture systems to recover and reintroduce any unused oxygen and/orhydrogen.

At least one embodiment is disclosed, and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R_(l), and an upperlimit, R_(u), is disclosed, any number falling within the range isspecifically disclosed. In particular, the following numbers within therange are specifically disclosed: R=R₁+k*(R_(u)−R_(l)), wherein k is avariable ranging from 1 percent to 100 percent with a 1 percentincrement, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent,96 percent, 95 percent, 98 percent, 99 percent, or 100 percent.Moreover, any numerical range defined by two R numbers as defined in theabove is also specifically disclosed. Use of the term “optionally” withrespect to any element of a claim means that the element is required, oralternatively, the element is not required, both alternatives beingwithin the scope of the claim. Use of broader terms such as comprises,includes, and having should be understood to provide support fornarrower terms such as consisting of, consisting essentially of, andcomprised substantially of. Accordingly, the scope of protection is notlimited by the description set out above but is defined by the claimsthat follow, that scope including all equivalents of the subject matterof the claims. Each and every claim is incorporated as furtherdisclosure into the specification and the claims are embodiment(s) ofthe present invention. Also, the phrases “at least one of A, B, and C”and “A and/or B and/or C” should each be interpreted to include only A,only B, only C, or any combination of A, B, and C.

What is claimed is:
 1. An unmanned aerial vehicle (UAV), comprising: afuselage; a propulsion system including an electric motor; and a fuelcell system configured to provide electricity to the electric motor, thefuel cell system comprising: a fuel cell including a cathode and ananode; a hydrogen tank configured to store hydrogen; an anode channelconfigured to supply hydrogen from the hydrogen tank to the anode; anoxygen tank configured to store oxygen; an air channel; a cathodeswitch, the cathode switch being in communication with the oxygen tankand the air channel, the cathode switch being configured to convertbetween an air mode, wherein the cathode switch permits air from the airchannel to pass therethrough, and an oxygen mode, wherein the cathodeswitch permits oxygen from the oxygen tank to pass therethrough; acathode channel configured to carry air from the cathode switch to thecathode when in the air mode and to carry oxygen from the cathode switchto the cathode when in the oxygen mode; and a processor programmed tocontrol the cathode switch, wherein the processor is programmed toautonomously convert the cathode switch between the oxygen mode and theair mode in response to at least one of the UAV operating above apredetermined altitude, the UAV moving faster than a predeterminedspeed, and the UAV climbing faster than a predetermined rate.
 2. The UAVof claim 1, wherein the processor is programmed to convert the cathodeswitch from the oxygen mode to the air mode when a condition that causedthe conversion to the oxygen mode is no longer satisfied.
 3. The UAV ofclaim 1, wherein the processor is programmed to convert the cathodeswitch from the air mode to the oxygen mode anytime power required bythe electric motor exceeds power generated by the fuel cell in the airmode.
 4. The UAV of claim 3, wherein the processor is programmed toconvert the cathode switch from the oxygen mode to the air mode anytimepower generated by the fuel cell in the air mode would exceed powerrequired by the electric motor.
 5. The UAV of claim 1, furthercomprising: a liquid cooling system configured to cool the fuel cell. 6.The UAV of claim 1, wherein the cathode switch is configured to redirectair flowing through the air channel to cool the fuel cell when thecathode switch is converted to the oxygen mode.
 7. The UAV of claim 1,further comprising: a plurality of sensors transmitting flight data tothe processor.